I thought t604 was harder than the 304 stuff but more likely to rust?

 

well, someone thats bored enough should do a little research and clear that up for those of us that are too lazy to do so.

 

Click and learn my friends.....

http://en.wikipedia.org/wiki/Stainless_steel

 

long read.
304 is the most common according to the wiki.

 

409 Stainless is generally considered a lower grade of stainless, but with very high durability and toughness. For this reason it is widely used in OEM exhaust applications. Although it can be polished, it is subject to "coloring" when exposed to high temperatures. 304 Stainless has a higher nickel content which allows it to accept and maintain a mirror like finish when polished. As always beauty has a price, and the higher nickel content makes the material more brittle and susceptible to cracking.

I don't think I've seen 604 used in automotive applications, but I've been wrong alot lately.

 

I have used 604 only in show car trailer queens. Looks great, PITA to work with. Special gas, special wire.